1. Field of the Invention
The present invention relates to an electromagnetic push-in starter, and especially to a starter which elastically pushes a pinion gear against the ring gear of an engine by means of a reciprocating shift lever which is linked to an electromagnetic switch.
2. Description of the Related Art
FIGS. 5 and 6 show the construction of a conventional starter. FIG. 5 is a cross-sectional view of the starter. FIG. 6 is a cross-sectional view along line 6--6 in FIG. 5. In FIG. 5, an electromagnetic switch 2 is mounted on a starter front bracket 1. The electromagnetic switch 2 ha a movable core 3 and a hook portion 3a is disposed at the leading end of the movable core, which is the end closest to the front bracket 1. A cam portion 4a of a shift lever 4 is engaged with the hook portion 3a. A cylindrical portion 4d is disposed in the central region of the shift lever 4. Another cam portion 4c is disposed at the end of the shift lever 4 opposite to the cam portion 4a, and is engaged with a clutch 21, which is connected to a pinion gear 22, and the cam portion 4c moves the clutch 21 in the direction of P whereby the pinion gear 22 is elastically pushed against and engaged with the ring gear of an engine (not shown).
In FIG. 6, a cylindrical portion 4d of the shift lever 4 is supported by a support wall 1a disposed in the front bracket 1, and is held between a disk-shaped plate 6 and the front bracket 1 by the elastic force of a lever spring 5, which is a coil spring.
In FIG. 5, the shift lever 4 is able to reciprocate around the cylindrical portion 4d or around the cam portion 4c. The lever spring 5 is supported by a yoke 7 by means of a plate 9 and a grommet 8.
A case 10 of magnetic material is disposed in the electromagnetic switch 2, and a bush 23 is inserted in an inner circumferential surface 10b of the end thereof, and is disposed such that the movable core 3 can slide along the inner circumferential surface of the bush 23 in the direction of P or Q. A pressure-bearing surface 3c for a spring 11, which is a coil spring for returning the movable core 3, is formed in a trailing end 3b of the movable core 3, which is the opposite end to the leading end where the hook portion 3a is disposed.
A fixed core 13, which form part of a magnetic circuit, is inserted into and secured to a socket joint portion 10a of the case 10. A movable contact shaft 12 is slidably supported by a round hole portion 13a of the fixed core 13. A solenoid 14, comprising an electromagnetic coil 16 wound around a bobbin 15, is disposed on the side of the fixed core 13 closest to the front bracket 1.
When a current is passed through the solenoid 14 by passing a current through a key switch (not shown), a magnetic circuit is formed which includes the movable core 3, the case 10, the fixed core 13, an air gap portion 17, and the movable core 3 is attracted towards the fixed core 13 and moves in the direction of Q. Accompanying this motion, the shift lever 4 rotates counterclockwise around the cylindrical portion 4d, and the cam portion 4c of the shift lever 4 pushes the clutch 21 which in turn elastically pushes the pinion gear 22 against the ring gear of an engine (not shown) to engage the pinion gear 22 with the ring gear, and at the same time the movable contact shaft 12 is pressed in the direction of Q, closing a contact circuit (not shown), and a motor 24 turns.
However, if the pinion gear 22 fails to engage with the ring gear of the engine and the counterclockwise motion of the shift lever 4 is obstructed as the movable core 3 is attracted toward the fixed core 13 and moves in the direction of Q, the shift lever 4 rotates counterclockwise around the cam portion 4c, the cylindrical portion 4d of the shift lever 4 moves in the direction of Q and presses again the lever spring 5 through the plate 6, and the lever spring 5 is compressed. The movable core 3 and the fixed core 13 come into contact and the movable contact shaft 12 is pressed, closing the contact circuit (not shown), and the motor 24 turns.
Because the conventional electromagnetic push-in starter is constructed in the above manner, when the pinion gear 22 and the ring gear of the engine fail to engage and the pinion gear is unable to move in the direction of P and stops, the shift lever 4 rotates counterclockwise around the cam 4c to ensure that the movable core 3 can move to press against the movable contact shaft 12. At this time, the cylindrical portion 4d of the shift lever 4 moves in the direction of Q and presses against the lever spring 5 through the plate 6. When the movable contact shaft 12 is pressed and the contact circuit (not shown) is closed and the motor 24 turns, the spring load in the lever spring 5 becomes the pushing force for the shift lever 4 which elastically pushes the pinion gear against the ring gear of the engine. Engagement of the pinion gear 22 in the ring gear is facilitated by this force.
The size of the starter, that is, the diameter of the motor 24 or the electromagnetic switch 2, can be reduced by a construction which decreases the center distance, which is the distance between the central axis 24a of the motor 24 and the central axis 2a of the electromagnetic switch 2. In order to decrease this distance, it is necessary to reduce the outside diameter of the lever spring 5. However, merely reducing the outside diameter of the lever spring 5 increases the stress on the lever spring 5, and there is a limit to the amount of reduction the outside diameter of the lever spring 5 can tolerate. Also, the load of the lever spring 5 pushing on the shift lever 4 is required to press the pinion gear 22 against the ring gear and cannot be decreased.